1. Field of the Invention
The present invention relates to a method and apparatus for producing high-purity hydrogen, and more particularly to a method and apparatus for recovering high-purity hydrogen from a pyrolysis gas, composed mainly of hydrogen and carbon monoxide, produced by pyrolysis of an organic material, for example, biomass such as waste wood or raw refuse.
2. Description of the Related Art
A pyrolysis gas, composed mainly of hydrogen and carbon monoxide, produced by pyrolysis of biomass such as waste wood or raw refuse is hydrogenated by steam reforming, and then hydrogen is separated and purified, and the purified hydrogen is effectively utilized as a fuel for a fuel cell. However, in a polymer electrolyte fuel cell which is expected as a technology close to utilization in recent years, because platinum is employed as a catalyst, it is necessary to make carbon monoxide contained in hydrogen almost zero. Therefore, gas reforming and purification for producing high-purity hydrogen is troublesome, and causes problems of operativity and economical efficiency.
In an electrolytic process which utilizes electric power generated by a pyrolysis gas, high-purity hydrogen can be produced by a relatively simple structure. However, this electrolytic process consumes a large amount of electric power.
On the other hand, there is a method of electrolyzing high-temperature steam at a high-temperature of 800° C. or higher. In this method, thermal energy is used to electrolyze water, thereby lowering electrolysis voltage to reduce the electrolysis power. However, this method needs to supplement 60% or more of electrolysis energy of water with electric power. As an improvement of the method of electrolyzing high-temperature steam, there has been proposed a method for lowering electrolysis voltage required for moving oxygen to an anode side of an electrolyzer by supplying natural gas to an anode of the electrolyzer in U.S. Pat. No. 6,051,125. This method is problematic in that expensive natural gas is consumed and it is necessary to take measures for preventing electrodes from being contaminated with carbon deposited by reaction of natural gas with oxygen. Therefore, the method proposed in U.S. Pat. No. 6,051,125 poses a problem in practical use.